Leviamon is a giant personal Digimon of Tactimon, & is co-piloted by MadLeomon.
It's by far the largest Digimon ever used, so large, in fact, that DoruGreymon (who is, itself, as large as a skyscraper) looks like a mosquito by comparison & Ebonwumon the Shuttle Digimon who can easily fit DoruGreymon on its back isn't even as big as Leviamon's foot. Leviamon has enough power to annihilate a planet. However, it is so massive that it requires tremendous energy, & is inactive much of the time. The fact that it keeps on running out of energy is the only reason why the DigiDestined ever survive a battle against it. It attacks by firing out bolts of energy, & its colossal size allows it to crush nearly any foe, although Ebonwumon the Shuttle Digimon can withstand that, if only barely.
Leviamon is first used when Tactimon takes it to the Deserted Dimension to keep the DigiDestined from getting the Sword of Light. Taylor briefly attempts to fight Leviamon with DoruGreymon, but quickly sees his Digimon is no match & retreats with Ebonwumon after Leviamon proves unable to crush it. Tactimon then goes on a rampage with Leviamon, destroying everything in sight, but he grows frustrated that he is unable to find the DigiDestined & decides to destroy the entire dimension. Fortunately, the DigiDestined manage to escape with the Sword of Light before Leviamon completely destroys the Deserted Dimension. Tactimon then takes Leviamon to Tokyo to destroy the city, but to his dismay finds that his Digimon had used up too much power & has to retreat back to his palace.
The only other time Leviamon does any fighting is when Tactimon creates Pachinkomon. While his Digimon is in Tokyo, Tactimon takes Leviamon to Earth. After Pachinkomon is destroyed by ThunderOmnimon, Leviamon arrives & disassembles the Digimon with one blast. Tactimon then attempts to crush DoruGreymon, but it hides inside Ebonwumon's shell. Tactimon tries to crush Ebonwumon, but somehow it drains over half of Leviamon's power, & Tactimon retreats back to his palace.
Leviamon is last used by Tactimon & Lilithmon to escape the moon when the Machine Empire attacks.